As shown in FIG. 5, what is known as a conventional acoustic wave duplexer is a surface acoustic wave duplexer that includes antenna terminal 101, transmission terminal 100, reception terminal 102, and phase circuit 200, in which transmission filter 2 and reception filter 3 are structured as a ladder type on piezoelectric substrate 1, using resonators 4, inductors 5 and the like.
As information on prior art documents related to the present application, Patent Document 1 is known, for example.
Conventionally, such an acoustic wave duplexer has been manufactured employing a rotated Y-cut lithium tantalate as piezoelectric substrate 1.
In recent years, various systems have been coming into use in mobile phones. As to those systems such as WCDMA Band 1 system, in which frequencies are widely separated between the transmission band of 1920 MHz to 1980 MHz and the reception band of 2110 MHz to 2170 MHz, the electromechanical coupling factor is insufficient. Therefore, it has been increasingly difficult to secure an enough attenuation amount of the duplex band and adequate isolation.